Needle-bar-moving speed changing mechanism for a sewing machine



Filed Feb. 2. 1968 Aug. 12, 1969'. YASUKATA H ET AL 3,460,498

- NEEDLE-BAR-MOVING SPEED CHANGING MECHANISM FOR A SEWING MACHINE INVORS YASUKATA EGUCH m KAZUO UCHIDA ATTORNEYS Aug. 12, 1969 YASUKATA cucmET AL 3,460,498

' NEEDLE-BAB-MOVING SPEED CHANGING MECHANISM FOR A SEWING MACHINE FiledFeb. 2, 1968 2 Sheets-Sheet 2 United States Patent Japan Filed Feb. 2,1968, Ser. No. 702,660 Claims priority, application Japan, Feb. 3, 1967,42/6 582 Int. Cl. D05b 69/ 00; F16h 21/22 U.S. Cl. 112221 4 ClaimsABSTRACT OF THE DISCLOSURE The present needle-bar speed changingmechanism is for use in zigzag sewing machines having a rotary uppershaft and a needle bar actuating mechanism including a balance crankfixed on said rotary upper shaft for turning therewith, a shaft on saidbalance crank, a needle bar, crank pivotally connected to said shaft, aneedle bar, a needle bar clamp connecting said needle bar to said needlebar crank and a reciprocating support carrying said needle bar wherebyturning movement to said needle bar crank imparts a reciprocatingmovement to said needle bar to enable a needle attached to said needlebar to perform a stitching operation and said needle-bar speed changingmechanism is interconnected in said sewing machine needle bar actuatingmechanism for delaying the upward movement of said needle-bar crankduring the operation of the sewing machine providing for an extendedperiod of coaction between the needle and the sewing machine shuttlehook on either the right or left side of the zigzag stitch.

Detailed description of invention The present invention relates to theneedle-bar-moving speed changing mechanism for a sewing machine and itsobjective is to offer a zigzag sewing machine in which the thread loopcan be reliably caught by the shuttle hook, even when the amplitude ofneedle bar oscillation is increased, thereby to obtain a beautifulzigzag stitching of big width.

It goes without saying that in a zigzag sewing machine an enlargedamplitude of oscillation of the needle bar mounted with a needle willresult in a broad zigzag stitching. The needle-bar mounted with a needlemakes a vertical movement and it becomes necessary to have the rotatingshuttle hook catch the thread loop formed beside the needle when theneedle penetrates the cloth to be stitched and again rises and passes acertain level, however, there is naturally a certain limitation to thezigzag movement of the needle in consideration of the thread loopcatching of the shuttle hook.

Namely, assuming that the needle moves vertically at a constant speed,while the shuttle rotates at a constant speed, there is only onemovement (one definite point) when a desirable condition occurs for theneedle and the shuttle hook to come across. Moreover an increasedamplitude of needle oscillation, i.e., an increased distance betweenright and left drop positions of the needle will inevitably defy thedesirable condition for the needle and the shuttle hook to come across.Thus, if you try to make the needle oscillate more widely to obtain awider zigzag stitching, it is self-evident that there is a certainlimitation. In order to eliminate such limitation to the thread loopcatching, several proposals have been made to limit the rotatingmovement of the shuttle or the vertical movement of the needle-bar,thereby assuring the desirable crossing condition of the needle and theshuttle hook to obtain more increased width of zigzag stitch. In

ice

these proposals, the composition is rather intricate and the manufactureand assembling becomes difficult and expensive, while the motion losessmoothness. Thus, these proposals will not always be applicable for asewing machine which is to be operated at high speed.

The present invention purports to eliminate this drawback of theconventional machine. Namely, the primary objective of this invention isto offer a relatively simple speed changing mechanism for the needle barof a sewing machine. According to this invention even when the amplitudeof needle oscillation is considerably enlarged, the appropriate crossingcondition of needle and the shuttle hook can be accurately maintainedthereby assuring a reliable catch of thread loop and in consequenceprecisely producing a beautiful, wider zigzag stitching. For thispurpose, according to this invention on the balance crank driven by therotation of the main shaft is loosely fitted the connecting shaft of theconnecting link connected to the needle-bar crank provided to drive theneedle-bar; a forked member is fixed to said connecting shaft; and anequal-width eccentric cam fixed to the machine frame is fitted into theforked part of said forked member. In this manner, the connectionbetween the needle-bar crank and the connecting link driven by therotation of the balance crank receives the action of said equal-widtheccentric cam; and in consequence the motion of the needle-barvertically moved by said needle-bar crank can be changed in speed at adesirable point of time; and by matching this point of speed change withthe crossing position of the needle and the shuttle hook a smoothcatching of thread loop can be realized and the needle oscillation forzigzag stitching can be enlarged. Moreover, the composition is extremelysimple with new additions of only an equal-Width eccentric cam and aforked member; the manufacture and assembly are both easy; and a widezigzag stitching can be realized without practically any rise in cost.

Another objective of this invention is to olfer a smooth- Working speedchanging mechanism as described above. Usually in the sewing machine therotating mechanism is preferably adopted and this ensures effectiveutilization of inertia as well as high-speed, smooth. action. Accordingto this invention, the rotation of the balance crank is absolutely thesame as that of the conventional machine; even when a forked engagingmember is adopted, said member moves as a single body together with saidbalance crank; and even if an equal-width eccentric cam is employed,said cam is fixed to the machine frame and said forked member makes asimple harmonic motion as it rotates around said cam. Thus, theacceleration of motion is limited with good transmission but with noincrease in the reciprocating mass; therefore, vibration does notincrease, no noise is generated; and hardly any wear is caused, therebyensuring very light movement for a long period.

More specific objectives and functional effects of this invention willbe more clearly understood from the description of an actual embodimentreferring to the attached drawings, in which:

FIG. 1 shows a front elevation of the needle-bar moving speed changingmechanism of this invention;

FIG. 2 shows a side view of the mechanism according to this inventionwith some parts in section and the front frame removed;

FIG. 3 shows an exploded oblique view of major component members of thisinvention;

FIG. 4 shows a diagram explaining the action of said mechanism of thisinvention; and

FIG. 5 shows a linear motion diagram of a needle bar equipped with thepresent invention and of the conventional needle bar, in reference tothread loop catching.

To explain an actual embodiment of this present invention, referring tothe accompanying drawings and particularly to FIG. 1, the machine frame50 holds a well known mechanism for vertically moving the needle-bar. Inthe illustrated embodiment, said mechanism for vertically moving theneedle bar consists of an upper shaft bushing 9 fitted to the bearing 51provided in one portion of said frame 50, and another bearing (notshown) provided in the rear portion of said frame 50, a balance crank Sfixed to one end of said upper shaft 4; a needle-bar crank 7 connectedat one end to said balance crank 5 by means of a connecting link 6; andat the other end connected to the needle bar by means of a needle barclamp 8 pivoted to said other end of said needle-bar crank 7. Saidneedle bar 10 is slidably supported by the support portions 11, 11 ofthe needle barsupport 13, the upper end of which is swingably held by apivot 14 at the forward edge of said frame 50. Said upper shaft 4, whenrotated by a suitable motion generating mechanism, rotates said balancecrank 5, which in turn causes the needle bar 10 to reciprocatingly movethrough said connecting link 6, said needle bar crank 7 and said needlebar clamp 8. At the midpoint of said needle bar support 13 is pivoted at16 one end of an oscillation rod extending from a well-known amplitudegenerating mechanism in the machine frame, said oscillation rod 15imparts an oscillation to said needle bar support 13 while said needlebar 10 is reciprocated by said motion generating mechanism as it issupported by said needle-bar support and thereby an amplitude for zigzagstitching is set to be produced. Adjacent said balance crank 5 thethread tensor arm 12 is rotatably mounted at its base portion on the pin6A of said connecting link 6 which is to be described hereinafter.Moreover, at the midpoint of said thread tensor arm 12 there is, asshown in FIG. 1, ivoted the tip of a restraining link 17, the baseportion of which is pivotally mounted on the seat 52 of the machineframe 50; and as is well known, the thread tensor arm 12 serves to feedthe upper thread to the needle 20 fixed to the lower end of the needlebar 10 and to tighten the stitch formed by the cooperation of the needle20 and the shuttle (not shown).

In this present invention, to achieve the above-mentioned specificobjects, the following members are added to the above-mentionedheretofore known arrangement. The upper shaft bushing 9 which is formedwith a flange 21 for securely fitting this bushing 9 into said bearing51, is extended to integrally constitute an equal width eccen- :trictriangular cam 1, which is fixed to said bearing 51 of the machine frame11 in such a manner that, as indi cated in FIG. 4, the shortest radiusof said eccentric cam 1 may come around the rotation angle 200 of theupper shaft 4 while the rotation angle 0 of the upper shaft 4corresponds to the upper dead point of said needle bar 10. Meanwhile,said pin 6A fixed to said connecting link 6 is rotatably inserted into ahole 22 formed at one end portion of said balance crank 5, and isextended at 6A to project on the back side of said balance crank 5. Onthis extended projection a forked member 2 is mounted by the fittinghole 3 formed at the lower end thereof, and then fastened by a screw 3.Said forked member 2 is arranged to receive said triangular cam 1.

In this present invention the aforementioned rotating angle 200 of uppershaft 4 usually corresponds to the time point when the favorablecondition is offered for the needle and the shuttle hook to cross eachother, especially when the needle is at the basic needle drop positionof the zigzag seam, which position is on the left side in this presentarrangement. Of course the phase of the equal-width eccentric cam can bevaried to match a different phase of any given sewing machine. Even whenthe shortest radius of the said equal-width eccentric triangular cam ispositioned around the rotating angle 200 of said upper shaft 4, thethread 100p catching by the shuttle hook at the left needle dropposition will never be adversely affected. Accordingly, the secure thebest condition for thread loop catching at the right needle drop, whichis the objective of this invention, the shortest radius of saidtriangular cam may be positioned within the scopes u to from 200 ofupper shaft rotation angles.

Of course said equal-width eccentric triangular cam 1 may be replaced byany other means so far as it serves this object, however, the presenteccentric cam 1 would be most effective to achieve such an object.

According to the arrangement of this present invention, a rotation ofsaid upper shaft 4 causes said balance crank 5 to move the connectingpin 6A around said upper shaft 4 on the locus 'y as indicated in FIG. 4and, therefore, said needle-bar crank 7 connected at the upper end tothe said link 6 by means of the connecting pin 6B is moved on a certainlocus, thereby to put said needle bar 10 into reciprocating movement;and at the same time said needle bar 10 is subject to the oscillatingmove ment effected by the aforementioned oscillation rod 15. In thismanner a good zigzag stitching is obtained with the appropriate relativecondition of the needle and the shuttle hook in which the thread loop isaccurately caught by the shuttle hook. To explain more precisely thefunction of the illustrated embodiment of this invention, said forkedmember 2 is turned by said balance crank 5 around said triangular cam 1and in the process of turning around said cam the forked member 2 issubjected to appropriate oscillation which turns said pin 6A in saidfitting hole 22 of the balance crank 5 and thereby to appropriatelydisplace the angle of said connecting link 6 with respect to saidbalance crank 5 which connecting link being fixed on the end of said pin6A in an opposite rotation to said forked member 2. Such angulardisplacement of said connecting link 6 operates to vary the upwardmovement of said needle bar crank 7 by retaining the same in the lowerposition for a preselected longer period of time whereby thereciprocating movement of the needle bar 10 is varied in speed tomaintain the favorable crossing condition for the needle and the shuttlehook to coact with each other even in a wider zigzag stitchingoperation.

To explain this operation of the present invention in more detail, inFIG. 4 taking the center of the pin 6A of the connecting link 6 or thecenter of the fitting hole 22 of the balance crank 5 for 0 and thecenter of the pin 6B by which the upper part of the needle-bar crank 7is connected to the connecting link 6 for 0 and with the equal-widtheccentric triangular cam 1 being fixed on the machine frame 11 in theabovementioned manner, the following relation will be established: Whenthe rotation angle of the upper shaft 4 is 200, center 0 is still thesame distance as is was before, or in other words, center 0 is on theturning locus 'y of the pin 6A; and while the upper shaft 4 rotates frompoint of 0=220, the center 0, of the pin 6A will shift from 0 (a) to 0(1)), and 0 will take the position of 0 (1)) as indicated by the solidline in FIG. 4, however, if this present invention is not applied,center 0 will move to 0 (1)) as it does at the conventional mechanism.According to this invention, however, since the forked member 2transmits the oscillation of said triangular cam ,1 to said pin 6A as itrotates around said triangular cam 1, said connecting link 6 is shiftedcounterclockwise by angle 8 around the center 0 (1)) when the uppershaft 4 rotates to angle 200. Thus, the reciprocal rotation of theconnecting link 6 restricts the rise of the needlebar crank 7 to aspecified extent as illustrated by angle in FIG. 4, and as the result ofrising motion of the needle-bar 10 is varied as indicated by the solidline in FIG. 5. The rotating angle 5 of the connecting link 6 may ofcourse be arbitrarily chosen by varying the lift L of the eccentric cam1, accordingly, the displaced decrement Ah of needle-bar movement at theright needle drop in FIG. 5 can be arbitrarily set. In FIG. 5, thebroken line represents the conventional movement of needle-bar incomparison with the solid line representing an example of the needle barmovement according to this present invention. In the illustratedembodiment of this present invention, as is understood from FIG. 5, theneedle at the left drop is at the position risen by fiL from its lowerdead point when the thread loop is favorably caught by the shuttle hook.This favorable condition for the needle and the shuttle hook to comeacross is generally obtained by the conventional sewing machinemechanism, because in the conventional mechanism, the upper shaftrotates 180 when the needle reaches the lower dead point, and the uppershaft rotates 200, the needle rises by said 5L from the lower dead pointand at that movement the thread loop is caught by the shuttle hook.However, as stated before, to displace the movement of the needle bar bydistance Ah within the range from 200 to 220 of the upper shaft rotationangles is to reduce the rising movement of the needle from the lowerdead point by distance Ah to distance 5R from distance 5R0. Thisreduction in the rising movement of the needle bar is, of course,effected when the needle is at the right side drop for the purpose ofarranging a favorable condition for the needle and the shuttle hook tocome across, and the thread loop is ready to be caught by the shuttlehook. In this manner the needle is prevented from going far above theshuttle hook when the lattercomes to catch the thread loop.

Thus, this present invention enables a wider zigzag stitching with highquality and smoothness.

Moreover, the present invention offers an extremely simple mechanismeasy to manufacture at low cost, which is the conventional mechanism towhich has been added an equal-width eccentric triangular cam 1 formed onthe upper shaft bushing 9 and a forked member 2 fixed to the pin 6A ofthe connecting link 6. The movement produced by said eccentricequal-Width triangular cam is a simple harmonic one with a limitedacceleration, and there is no increased reciprocating mass involved;accordingly, the transmission is excellent, the durability, which ismost important from the industrial point of view, is assured, no noiseis generated in position, and there is little wear of parts, so that anextremely long service life is guaranteed.

The present invention is also applicable to a straight stitch sewingmachine; it will fully compensate for a certain error in the relativetiming movement of needle and shuttle and assure an appropriate threadloop catching, thereby contributing to the undesirable elimination ofthe stitch skip phenomenon.

What we claim is:

1. In a needle-bar actuating mechanism of a sewing machine having arotary upper shaft, said actuating mechanism including a balance crankfixedly mounted on said rotary upper shaft, a shaft mounted on saidbalance crank and adapted to be turned in accordance with the turningmovement of said balance crank, a needle-bar crank pivotally connectedat one end thereof to said shaft, a needle bar, a needle bar clampconnecting said needle bar to the other end of said needle bar crank anda reciprocating support carrying said needle bar whereby a turningmovement is imported to one end of said needle bar crank when saidbalance crank is turned, thereby imparting a reciprocating movement tosaid needle bar and enabling a needle attached to the lower end of saidneedle bar to perform a stitching operation, a needle bar moving speedchanging mechanism comprising a connection link having a first pincomprising said shaft on said balance crank mounted on one side and .asecond pin mounted on the other side thereof, said first pin beingrotatably connected to one end of said needle bar crank and said secondpin being rotatably fitted through a hole formed in said balance crankand protruding from the other side of said balance crank, a forkedmember fixedly mounted to said protruding end of said second pin, anequal-width eccentric cam fixedly provided on the machine frame andengaging with said forked member, said equal-width eccentric cam beingarranged in such a manner that the shortest radius thereof is sopositioned with respect to said machine frame to vary the rotary outputof said first pin through the engagement of said cam, whereby the upwardmovement of the needle bar crank is delayed thereby providing for anextended period of coaction between the needle and the shuttle book.

2. A needle bar actuating mechanism as set forth in claim 1, includingan oscillation rod connected at one end thereof to said needle barsupport and connected at the other end thereof to an oscillationgenerating mechanism so as to oscillate said needle bar and to enable itto perform a zigzag stitching operation, said equal width eccentric cambeing selectively positioned to provide for said extended period ofcoaction between the needle and shuttle hook on either the right or leftside of said zigzag stitch.

3. A needle bar actuating mechanism as set forth in claim 1, including abushing journaled in a portion of said machine frame, said equal-widtheccentric cam being formed integrally with said bushing, said bushingrotatalhhf/ receiving and horizontally supporting said upper s a t.

4. A needle bar actuating mechanism as set forth in claim 3, whereinsaid equal-width eccentric cam is a triangular cam.

References Cited UNITED STATES PATENTS 29,035 7/1860 First l12-22l769,039 8/ 1904 Abercrombie 112-22l 2,883,951 4/1959 Amman 112-221 H.HAMPTON HUNTER, Primary Examiner US. Cl. X.R. 74-44

